Creating a repository with "Allow only private forks" option results in that option set to "Allow forks"

Issue Summary

When forking a repository with "Allow only private forks", the resulting Fork will be private as expected. However on this private Fork, under repository Details > Advanced, further Forking will have the option selected by default  "Allow forks". This means that after that, any user will have the ability to create a Private or Public Fork from there. 

Steps to Reproduce

1. Within existing repository details, select Advanced > Forking > Allow only Private forks
2. After that, navigate to repository Source > "..." >  Fork this repository
3. Forked repository will be created as Private as expected 
4. On the Forked repository, Go to the repository settings > Repository Details > Advanced 
5. Forking option will have "Allow Forks" selected, this means both Private and Public forks are possible

Ask for improvement 

For any forked repos that were created off the repo with "Allow only Private forks" setting, the ask that by default the option selected for the forked repo should be "Allow only Private forks" too.

Also add additional options when Fork is created to be configurable by Admins: 

• "Prevent creating a fork of a fork"
• "Only allow forks within the same workspace as parent repo"

Workaround

After a Fork is created, owner of the forked repo can manually set forking preferences on the repo, to allow all forks or only Private forks.